Automatic transmissions have been utilized for various drive systems, such as in automobiles to allow for ease in driving. The demand for such an automatic transmission has been accordingly increasing from year to year. Conventional automatic transmissions utilize fluid torque converter systems. However, such a system is disadvantageous in many respects such as poor power transmission efficiency and complicated construction which leads to higher production costs.
Conventional V-belt type transmissions have been utilized as an alternative. In conventional belt-type transmissions, it is necessary to employ pulleys whose effective pitch diameter is small in order to obtain a large transmission ratio. For example, if maximum torque is required to drive the automobile, the effective pitch diameter of a driver speed change pulley must be small as compared to that of a driven speed change pulley so that the reduction ratio is increased. This is required due to the fact that in order to obtain a high speed, it is necessary to use a driver pulley whose diameter is large and a driven pulley whose diameter is small, which causes a V-belt spanned between the pulleys to rotate at a high speed. Therefore, it is necessary to adjust the effective pitch diameter of the driver pulley so that the V-belt may be rotated at a maximum allowable limit. Theoretically, the minimum diameter of the driven pulley must be larger than the minimum allowable limit. Inevitably, in such a conventional V-belt type power transmission system, a narrow speed change range results.
The present invention has been developed to overcome the above-described problems of prior power transmission systems.